1. Field of the Invention
This invention relates to compositions of polypropylene and grafted propylene copolymer. More specifically, the invention relates to multi-phase compositions having improved properties comprising polypropylene, a non-compatible polymer and/or filler and a propylene-ethylene copolymer grafted with carboxylic acids or derivatives. Preferably the grafted propylene-ethylene copolymer is an impact copolymer having a high graft concentration and relatively low melt flow rate.
2. Description of the Prior Art
Multi-phase polypropylene (PP) compositions are widely utilized for a variety of applications. For example, PP is commonly combined with non-compatible polymers, such as polyamides and ethylene-vinyl alcohol (EVOH) copolymers, to provide compositions suitable for films, coatings and moldings having improved barrier and physical properties. Similarly, PP and engineering thermoplastics are often blended to produce compositions and molded articles having improved mechanical properties. In other instances, various filler materials, such as mineral fillers, glass fibers and cellulosic fibers, are incorporated into PP to provide reinforced compositions having a desired balance of stiffness, impact strength, etc. For certain other applications, hydrated inorganic fillers are included in PP compositions to reduce flammability. In still other instances PP is combined with both a non-compatible polymer and filler material, e.g., nylons and glass fibers, to produce reinforced polymer composites.
With compositions of the above types it is a widely accepted practice to include one or more functionalized compounds, commonly referred to as coupling agents and/or compatibilizing agents, to facilitate dispersion and/or bonding of the non-compatible polymers and/or filler material with the non-polar PP polymer. In general, it is believed that the functionalized compounds interact at the interface of the components to enhance compatibility of the additive component(s) and thus increase their desirable affect and provide composites having improved properties. Functionalized compounds commonly employed as coupling/compatibilizing agents are often olefin polymers grafted with ethyleneically unsaturated carboxylic acids, hydrogenated vinyl aromatic/conjugated diene block copolymers grafted with ethylenically unsaturated carboxylic acids, olefin/acrylic ester/ethylenically unsaturated carboxylic acid terpolymers and olefin/acrylic ester/glycidyl acrylate terpolymers.
Functionalized propylene-ethylene copolymers have been disclosed as coupling/compatibilizing agents for PP compositions. Published International Publication No. WO 02/059196 A1 discloses wood fiber-filled PP compositions having improved stiffness strength and creep resistance and articles fabricated therefrom. The compositions contain 40–70 weight percent (wt. %) crystalline propylene polymer of specified NMR tacticity index and molecular weight distribution (MWD), 20–60 wt. % wood fiber and 0.3–12 wt. % functionalized olefin polymer. Whereas functionalized homopolymers of propylene are preferred, copolymers of propylene with another α-olefin, such as ethylene, are also mentioned.
Fiber-reinforced polymer compositions containing 30–90 wt. % polyamide, 5–50 wt. % glass fibers and 10–70 wt. % polyolefin, of which a portion can be an unsaturated carboxylic acid-modified polyolefin, are disclosed in U.S. Pat. No. 4,990,550. The reference indicates that the polyolefins to be modified with unsaturated carboxylic acids or their derivatives are not limited to homopolymers of α-olefins but include copolymers of different α-olefins. Random and block copolymers of propylene and other α-olefins, most notably ethylene, wherein the propylene content is 50 mol % or more and, more preferably, 80 mol % or more are specifically mentioned.
Glass-filled polyolefin compositions comprising propylene polymers of specified tacticity and MWD, an ethylene/C4-6 α-olefin plastomer and functionalized olefin polymer compatibility agent are also disclosed in International Publication No. WO 97/33941. Graft copolymers of propylene polymers with maleic acid are disclosed and the reference further indicates the propylene polymer portion of the graft can be a homopolymer of propylene or a copolymer of propylene with another α-olefin such as ethylene.
U.S. Pat. No. 5,514,745 discloses glass fiber reinforced molding mixtures which consist of a long glass fiber reinforced PP masterbatch and a PP resin. The long glass fiber reinforced PP is produced using glass fibers surface-finished with a finishing agent containing a coupling agent which is impregnated with a modified PP having functionality capable of reacting with the coupling agent. Carboxylic acid and anhydride-modified PP resins are disclosed as useful modified PPs for this purpose.
Polyamide/olefin polymer blend compositions containing a plurality of compatibilizing agents are disclosed in U.S. Pat. No. 5,317,059. For these compositions, which preferably are a combination of polyamide with polypropylene or a copolymer of propylene and ethylene, a first compatibilizing agent which is a terpolymer of an α-olefin, an acrylic ester and an alpha, beta-olefinically unsaturated dicarboxylic acid or glycidyl acrylate and an auxiliary compatibilizing agent selected from the group consisting of (a) at least one selectively hydrogenated block copolymer of a vinyl aromatic hydrocarbon and a conjugated diene to which has been grafted, an alpha, beta-olefinically unsaturated carboxylic acid reagent; (b) at least one polymer which is the product of the reaction of an alpha-olefin polymer and an alpha-beta-olefinically unsaturated carboxylic acid reagent; and (c) a mixture of the first compatibilizing agent with (a) and/or (b) reacted in the presence of a radical initiator. Ethylene-propylene elastomers grafted with maleic anhydride are mentioned as a type of auxiliary compatibilizing agent which can be used for the invention.
U.S. Pat. No. 5,324,755 discloses the use of polyethylene, polypropylene and copolymers of ethylene and propylene which have been chemically modified with ethyleneically unsaturated carboxylic acid or derivatives as coupling agents in compositions with propylene polymers grafted with styrenic monomer, glass fiber and, optionally, one or more rubber polymer component.
Published U.S. Patent Application U.S. 2001/0033924 A1 discloses nanocomposite concentrate compositions comprised of a layered silicate material and a polyolefin matrix polymer. The polyolefin matrix polymer is comprised of maleic anhydride-modified polyolefin and unmodified polyolefin. The layered silicate is intercalated with the matrix polymer which can be in the form of a polymer or oligomer capable of polymerization to form the polymer. The reference indicates that impact copolymers containing ethylene-propylene rubber can be used as the matrix polymer and polymer intercalate for the invention.
Whereas compositions containing maleic anhydride-modified propylene polymer coupling/compatibilizing agents have been disclosed in the prior art, there is a continuing need for propylene polymer compositions having improved properties. This and other objectives are achieved with the compositions of the present invention which are described in more detail to follow.